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Astron. Astrophys. 351, 31-42 (1999)

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Structure of the broad-line region of 3C 273 *

M. Dietrich 1, S.J. Wagner 1,2, T.J.-L. Courvoisier 3,4, H. Bock 1 and P. North 5

1 Landessternwarte Heidelberg, Königstuhl, 69117 Heidelberg, Germany
2 MSSSO, Private Bag, Weston, ACT 2611, Australia
3 INTEGRAL Science Data Centre, Chemin d'Ecogia 16, 1290 Versoix, Switzerland
4 Geneva Observatory, 1290 Sauverny, Switzerland
5 Institut d'Astronomie de l'Université de Lausanne, Observatoire, 1290 Chavannes-des-Bois, Switzerland

Received 30 December 1998 / Accepted 16 September 1999

Abstract

The number of discrete emitters in broad-line region cloud models of active galactic nuclei is still unknown. A finite number of clouds will cause intrinsic fluctuations in the emission line profiles. We observed the quasar 3C 273 with high spectral resolution (R[FORMULA]10 km s-1) and high signal to noise ratio to estimate the number of individual emitters in the broad-line region. The residua of the emission-line wings of the low ionization lines H[FORMULA] and H[FORMULA] were cross-correlated. We compared the results of the cross-correlation analysis with models of different cloud distributions. The smoothness of the line profiles implies lower limits to the number of individual clouds and to the width of the line profiles of these clouds. For emitters with a line profile width of FWHM [FORMULA] 15 km s-1 corresponding to a temperature of Te [FORMULA]2 104 K, we found that the number of clouds is larger than Ncl = 108. For clouds of significantly larger individual profile width (FWHM [FORMULA] 100 km s-1) it is found that the number of clouds can be of the order of [FORMULA]108. Since the number of individual emitters is several orders of magnitude larger than the number of stars involved in bloated star models these models can be ruled out as dominant source for broad-line region clouds. However, the non-detection of a cross-correlation signal is consistent with BLR models which assume a continuous hydrodynamical flow as source of the line emitting material.

Key words: galaxies: active – galaxies: quasars: emission lines – galaxies: quasars: individual: 3C 273

* Based on observations collected at the European Southern Observatory, La Silla, Chile

Send offprint requests to: M.Dietrich (mdietric@lsw.uni-heidelberg.de)

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© European Southern Observatory (ESO) 1999

Online publication: November 2, 1999
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